Intraocular lenses (IOLs) are now accepted treatment for cataracts in older children and are being used increasingly in younger children and even infants, but little is known about the safety or the appropriate power to implant in a rapidly growing eye. Available data suggest that a fair-to-good visual acuity outcome can be more consistently obtained in infants with a unilateral congenital cataract who undergo IOL implantation at the time of cataract surgery, but the methods used to assess the visual outcome in these series have been nonstandardized and may have overestimated the visual acuity of the pseudophakic eyes. Moreover, these series have generally reported more complications in pseudophakic than aphakic eyes. Therefore, the question - What is the best way to treat infants with unilateral aphakia? - remains unanswered. The objective of this randomized multicenter clinical trial is to compare two treatments for infants with a unilateral congenital cataract. The control group will receive the conventional treatment that involves cataract surgery followed by optical treatment with a contact lens and later coupled with spectacle treatment. The experimental group will also undergo cataract surgery but in addition will have an IOL implanted during the same surgery. The IOL will serve as the primary optical treatment any residual refractive error will be corrected with spectacles. This randomized, multi-center clinical trial will: 1) determine whether infants with a unilateral congenital cataract are more likely to have an interocular acuity difference of less than 0.2 LogMAR when 12 months of age if they undergo primary implantation of an IOL or if they are corrected primarily with a contact lens; 2) determine whether more complications develop and reoperations are necessary in eyes undergoing the primary implantation of an IOL; and 3) determine whether parents of infants with a unilateral congenital cataract experience less parenting stress if their child is primarily treated with an IOL. The public health importance of this trial not only involves the approximately 300 children born each year in the United States with a unilateral congenital cataract, but also the many more children born each year with bilateral cataracts or who acquire a cataract during early childhood.